Cultivated and commercial forms of tomato generally belong to a species most frequently referred to as Lycopersicon esculentum Miller (also known as Solanum lycopersicum) that is grown for its fruit and which is widely used as a fresh market or processed product. As a crop, tomato is grown commercially wherever environmental conditions permit the production of an economically viable yield. The size of tomato fruits may range from small to large and there are cherry, plum, pear, standard, and beefsteak types. Tomatoes may be grouped by the amount of time it takes for the plants to mature fruit for harvest; in general the cultivars are considered to be early, midseason or late-maturing. Tomatoes can also be grouped by the plant's growth habit, which can be determinate or indeterminate. Determinate plants tend to grow their foliage first, then set flowers that mature into fruit if pollination is successful. All of the fruit tend to ripen on a plant at about the same time. Indeterminate tomatoes start out by growing some foliage, then continue to produce foliage and flowers throughout the growing season. These plants will tend to have tomato fruit in different stages of maturity at any given time. More recent developments in tomato breeding have led to a wider array of fruit color. In addition to the standard red ripe color, tomatoes can be creamy white, lime green, pink, yellow, golden, or orange.
The first largest processing market and second largest fresh market for tomatoes in the United States is in California, where processing tomatoes are harvested by machine. The majority of fresh market tomatoes are harvested by hand at vine ripe and mature green stages of ripeness. Fresh market tomatoes are available in the United States year round. Process tomato season in California is from late June to October. Process tomatoes are used in many forms, as canned tomatoes, tomato juice, tomato sauce, puree, paste and catsup. Of the 500,000 acres of tomatoes that are grown annually in the US, approximately 40% are grown for fresh market consumption, while the remaining are grown for processing.
Lycopersicon is a relatively small genus within the extremely large and diverse family Solanaceae, which is considered to consist of around 90 genera including pepper, tobacco, and eggplant. The genus Lycopersicon has been divided into two subgenera, the esculentum complex which contains those species that can easily be crossed with the commercial tomato and the peruvianum complex which contains those species which are crossed with considerable difficulty (Stevens, M., and Rick, C. M. 1986. Genetics and Breeding. In: The Tomato Crop. A scientific basis for improvement, pp. 35-109. Atherton, J., Rudich, G. (eds.). Chapman and Hall, New York). Due to its value as a crop, L. esculentum Miller has become widely disseminated all over the world. Even if the precise origin of the cultivated tomato is still somewhat unclear, it seems to come from the Americas, being native to Ecuador, Peru and the Galapagos Islands and initially cultivated by Aztecs and Incas as early as 700 AD. Mexico appears to have been the site of domestication and the source of the earliest introduction. It is thought that the cherry tomato, L. esculentum var. cerasiforme, is the direct ancestor of modern cultivated forms.
Tomato grafting has been utilized in Asia and Europe for greenhouse and high tunnel production and is gaining popularity in the United States. One advantage of grafting is that rootstocks may be used that provide or increase resistance against, for example, fungal and viral diseases. In addition to providing or increasing resistance against such diseases, the use of grafting may also increase tolerance against different abiotic stresses, such as drought tolerance, salinity tolerance, flooding/water tolerance and heat and cold temperature tolerance. There are several methods for grafting tomatoes. The most common grafting methods include tongue approach/approach graft, hole insertion/terminal/top insertion graft, one cotyledon/slant/splice/tube graft, and cleft/side insertion graft.
Tomato is a simple diploid species with twelve pairs of differentiated chromosomes. The cultivated tomato is self-fertile and almost exclusively self-pollinating. The tomato flowers are hermaphrodites. Commercial cultivars were initially open-pollinated, but most have now been replaced by better yielding hybrids. Due to its wide dissemination and high value, tomato has been intensively bred.
It is becoming more and more challenging for farmers globally to satisfy the increasing worldwide demand for food. Progressively adverse environmental conditions steadily decrease available arable land. Furthermore, a growing global population presents serious challenges to the agricultural industry. Thus, there is a need to overcome the current constraints (e.g., land, water, etc.) and reduce the risks of climate volatility. Improving crop production is essential to the future of sustainable agriculture.
Current agricultural systems use traditional breeding methods or transgenic technologies to develop improved plant varieties. Presently lacking is a breeding method which places emphasis on the plant organ (the root) responsible for supplying vital nutrients to the plant, thus directly impacting the plant's ultimate performance, yield, and its ability to tolerate abiotic stress.
Tomato is an important and valuable vegetable crop. Thus, there is a continued need for new tomato varieties. In particular, there is a need for an improved non-GMO tomato rootstock variety that is stable, high yielding, and agronomically sound. A rootstock variety that is tolerant to abiotic stress conditions (for example, cold, heat, salinity and/or drought) and can overcome sub-optimal growing conditions that limit crop yield, for example for growing processing tomatoes, is also needed.